Effects of body size and countermeasure exercise on estimates of life support resources during all-female crewed exploration missions.

Employing a methodology reported in a recent theoretical study on male astronauts, this study estimated the effects of body size and aerobic countermeasure (CM) exercise in a four-person, all-female crew composed of individuals drawn from a stature range (1.50- to 1.90-m) representative of current space agency requirements (which exist for stature, but not for body mass) upon total energy expenditure (TEE), oxygen (O) consumption, carbon dioxide (CO) and metabolic heat (H) production, and water requirements for hydration, during space exploration missions. Assuming geometric similarity across the stature range, estimates were derived using available female astronaut data (mean age: 40-years; BMI: 22.7-kg·m; resting VO and VO: 3.3- and 40.5-mL·kg·min) on 30- and 1080-day missions, without and with, ISS-like countermeasure exercise (modelled as 2 × 30-min aerobic exercise at 75% VO, 6-day·week). Where spaceflight-specific data/equations were not available, terrestrial equivalents were used. Body size alone increased 24-h TEE (+ 30%), O consumption (+ 60%), CO (+ 60%) and H (+ 60%) production, and water requirements (+ 17%). With CM exercise, the increases were + 25-31%, + 29%, + 32%, + 38% and + 17-25% across the stature range. Compared to the previous study of theoretical male astronauts, the effect of body size on TEE was markedly less in females, and, at equivalent statures, all parameter estimates were lower for females, with relative differences ranging from -5% to -29%. When compared at the 50th percentile for stature for US females and males, these differences increased to - 11% to - 41% and translated to larger reductions in TEE, O and water requirements, and less CO and H during 1080-day missions using CM exercise. Differences between female and male theoretical astronauts result from lower resting and exercising O requirements (based on available astronaut data) of female astronauts, who are lighter than male astronauts at equivalent statures and have lower relative VO values. These data, combined with the current move towards smaller diameter space habitat modules, point to a number of potential advantages of all-female crews during future human space exploration missions.